Release of Nutrients and Trace Elements from Wood-, Agricultural Residue- and Manure-Based Biochars

Abstract

Biochar has been used in many applications as a remediation material, but less attention has been paid to the potential release of various soluble components that may alter the effectiveness of the remediation process. Here, we report the release of nutrients, trace elements, anions and cations from 36 types of biochars. A batch-style experiment was performed by mixing biochar and water at a mass ratio of 1:75. Elevated concentrations of these components were observed in the majority of the solutions mixed with the biochars. No significant differences were observed between low-temperature (low-T, 300 °C) and high-temperature (high-T, 600 °C) biochars in terms of NO3−, Cl−, Na+, Ca2+, Fe, Cu, PO4-P, NH3-N, and K+ concentrations (P < 0.05). Agricultural residue biochars released significantly less Cl−, Na+, Mn, Ca2+, and K+ than manure-based biochars. The observation of nutrients and metal ions in solution was supported by the results of scanning electron microscope/energy-dispersive X-ray (SEM/EDX) analysis. The release of elevated concentrations of anions, cations, trace elements, and nutrients may affect receiving water bodies after the application of biochar.